1. Field of the Invention
The present invention relates to the fabrication of high strength, creep resistant, structural components using reinforcing fibers, and more particularly to light-weight, porous, composite structural components incorporating high strength, hollow reinforcing fibers, a method for making the fibers and products made using the fibers for reinforcing the composite materials.
2. Background of the Invention
The need for new materials with high specific strength and creep resistance has prompted development of advanced methodologies for obtaining enhanced composite materials. A large portion of these efforts have been centered around the use of continuous fibers for reinforcement of ceramic and metal matrix composites.
It is well-known to use fiber reinforcement systems in composite materials for enhancing the strength and stiffness properties exhibited by those materials. For many years, the most commonly used fibers in the aerospace Industry were solid with a substantially circular cross section.
Very recently hollow fibers exhibiting improved mechanical properties have been developed. Such hollow fibers have been considered especially useful in augmenting compressive strength. Various processes for the production of hollow fibers are known. For example, U.S. Pat. No. 4,175,153 to Dobo et al. teaches various processes for making, and applications for using, hollow fibers in the production of substantially pure hydrogen. Composites using these hollow fibers are embodied as membranes and membrane support structures for gas diffusion or fluid separation application, as well as apparatus for fuel cell and other catalyzed reactions. The inorganic materials of which the Dobo et al. fibers are made include metals such as the hydrogen diffusible, noble metals (eg. iron, nickel and their alloys). The sinterable inorganic materials can be ceramics, such as aluminum oxide and b-alumina, or cermets or mercers, such as iron metal/aluminum oxide and nickel metal/titanium carbide.
In the aerospace industry, however, reinforcement fibers, both solid and hollow, are typically selected from organic materials (eg., glass, carbon or aramid), ceramic materials, (eg, quartz, alumina or silicon carbide) and metallic materials. Of these choices, reinforcement fiber systems made of ceramic materials are favored for their ability to withstand high temperatures and to provide excellent insulation against extreme heat. For example, it is known that a silicon carbide (SiC) fiber can retain significant strength above 1800.degree. F. (980.degree. C.), and that the SiC material offers high heat resistance up to 2200.degree. F. (1200.degree. C.). In addition, SiC exhibits excellent wetting properties and oxidative resistance allowing fibers of this material to reinforce polymers, polyimides, ceramics and metals.
With all this knowledge, nevertheless there is still a great need for an improved structural material including a metal matrix composition incorporating a fiber-reinforcing system which yields a light weight, high strength, creep resistant composite material and which is porous to the extent that It enables liquid or gas flow through preselected regions of the material.